Reviews

ABSTRACT: The staging of lung cancer defines the extent of disease. Accurate staging is important to define operability, select treatment regimens, and predict survival. Nonsurgical and surgical techniques are used to stage patients. The most important nonsurgical techniques used currently are the chest x-ray and computed tomographic (CT) scan of the chest and upper abdomen. In the future, positron emission tomography (PET) may become the single most important nonsurgical investigation. Surgical staging involves histologic assessment of the primary tumor and potential sites of metastases. At present, the standard for surgical staging is cervical mediastinotomy. Other minimally invasive surgical procedures used to stage patients with lung cancer are scalene lymph node biopsy, bronchoscopy with transbronchial biopsy, anterior mediastinoscopy, and video-assisted thoracoscopy. The different surgical staging options and their indications will be discussed in depth. [ONCOLOGY 13(5):679-685, 1999]

Introduction

The staging of lung cancer defines the extent of the disease. Accurate staging is crucial for defining operability, selecting treatment regimens, and predicting survival. Lung cancer staging is based on the American Joint Committee for Cancer (AJCC) TNM (tumor, node, and metastases) system, which describes the greatest anatomic extent of disease (Table 1).[1]

TABLE 1TNM Staging of Lung Cancer

Nonsurgical and surgical techniques are used to stage patients. All preoperative techniques are clinical. Operative and postoperative information provides the pathologic stage. A proper history and physical examination are mandatory.

Noninvasive Imaging Techniques

Chest x-ray and computed tomographic (CT) scan of the chest wall and upper abdomen are the most frequent imaging investigations used prior to diagnosis. The chest x-ray provides information pertaining to the size and location of the tumor, secondary effects to the remaining lung, hilar adenopathy, and metastatic disease involving the skeletal structures.

Computed tomography defines more accurately the size, location, and characteristics of the tumor, local extension into contiguous structures, lymphadenopathy, and metastatic disease to the liver and adrenal glands. Although the CT scan is very helpful as an initial screen, it is relatively insensitive in detecting invasion, as compared with surgical staging.[2] Several studies have demonstrated that CT scans have a sensitivity of 79% for identifying positive mediastinal adenopathy. The specificity of CT for detecting metastatic lung cancer is even lower (65%) when compared to surgical staging.[3] Computed tomography is approximately 85% accurate in predicting malignant lymph nodes when these nodes are greater than 1.5 cm in size.[4]

The data suggest that the CT scan should be used as an initial investigation in clinical staging. Its findings can then be confirmed with selective minimally invasive staging procedures.

Surgical Staging

Surgical staging involves histologic assessment of the primary tumor and potential sites of metastases. T1 and T2 lesions are based on size and lobar atelectasis or pneumonia.

Lesions found within 2 cm of the carina but not involving the carina are considered T3 lesions. T3 lesions also include those tumors that involve structures amenable to resection; these include the parietal pleura, chest wall, diaphragm, mediastinal pleura, mediastinal fat, pericardium, phrenic nerve, and sympathetic chain. Lesions that cause obstructive pneumonia or atelectasis of the entire lung are also considered T3 tumors.

T4 lesions are those that invade structures not amenable to resection, including the heart, great vessels, esophagus, vertebral body, carina, and trachea, as well as tumors that are associated with a malignant pleural effusion. Determinants of T3 and T4 lesions can be identified via minimally invasive surgical procedures.

The most common metastatic sites are the regional lymph nodes. N1 disease includes the ipsilateral segmental and peribronchial lymph nodes. These nodes are resected with an anatomic lung resection. N2 nodes are located in the ipsilateral mediastinum or subcarina. Extension of disease to the contralateral mediastinal, scalene, or supraclavicular lymph nodes is considered to be N3 disease.

FIGURE 1Regional Nodal Stations for Lung Cancer Staging

A lymph node map developed by the American Thoracic Society provides a numbering system to identify the lymph node groups in the lung and mediastinum (Figure 1).[5] This map can be used to record and classify the extent of lymph node metastases assessed radiographically, surgically, and pathologically.

Surgical procedures used in the staging of lung cancer are scalene node biopsy, bronchoscopy, cervical mediastinoscopy, anterior mediastinotomy, and thoracoscopy. These different options and their indications will be discussed in depth.

Scalene Lymph Node Biopsy

Daniels was the first to describe scalene lymph node biopsy in 1949.[6] This technique was used to define extrathoracic disease in patients with lung cancer, and biopsies were commonly performed without palpable lymphadenopathy. Scalene lymph node biopsy was widely used prior to the advent of cervical mediastinoscopy in patients suspected of having inoperable bronchogenic carcinoma.

A palpable scalene lymph node should be subjected to a fine-needle aspiration biopsy. Controversy remains concerning nonpalpable, blind lymph node biopsy. This procedure is seldom done routinely but may be appropriate in selected situations.

Lee and Ginsberg suggest that ipsilateral scalene lymph node biopsy should accompany cervical mediastinoscopy in patients who are being considered for combined-modality therapy that includes surgery.[7] Their approach involves scalene lymph node biopsy (prescalene fat pad) through the same suprasternal notch incision used for mediastinoscopy. In patients determined to have N2 disease by mediastinoscopy, the scalene node biopsy harbored occult nonclinical involvement in 15.4% of cases; 68.4% of patients with N3 were found to have occult involvement of the scalene lymph nodes. There may be a selected role for scalene node biopsy in patients with N2 disease who are being considered for combined-modality therapy and in patients with superior sulcus tumors.

The Technique—Scalene node biopsy can be performed under local or general anesthesia. The incision is made over the palpable lymph node or, if the nodes are nonpalpable, over the ipsilateral side of the lung lesion. A 2-cm incision is made 2 cm above the clavicle over the lateral border of the sternocleidomastoid muscle. The omohyoid muscle is retracted superiorly and laterally.

The borders of the dissection are the jugular vein medially, the omohyoid muscle superiorly and laterally, and the subclavian vein inferiorly, which is usually not clearly identified. The entire fat pad is excised.[7] Often, the transcervical artery requires division, and the phrenic nerve should be avoided. The thoracic duct must be ligated if injured.

When scalene lymph node biopsy is combined with cervical mediastinoscopy, the same incision is used (ie, a 2- to 3-cm incision 1 cm superior to the suprasternal notch). After the cervical mediastinoscopy has been performed, the mediastinoscope is directed posterolaterally and superiorly behind the carotid sheath into the supraclavicular fossa. Using careful blunt dissection of the medial aspect of the fat pad, biopsies are performed.

Complications—Rare complications that may be associated with this procedure are pneumothorax, arteriovenous fistula, and damage to the phrenic nerve.

Bronchoscopy

Flexible fiberoptic bronchoscopy is a reliable, safe technique for the evaluation and staging of lung cancer. This procedure can be performed as an outpatient procedure while the patient is under local anesthesia.

Bronchoscopy provides a visual assessment of an endobronchial tumor and may identify an unexpected primary tumor or a second primary lesion.

As mentioned previously, tumors that involve the trachea or carina are staged as T4. Tumors within 2 cm of the carina are defined as T3. Tumors involving the origin of the right upper lobe bronchus can be assessed with respect to performing a sleeve right upper lobectomy or right pneumonectomy.[8] These procedures involve the removal of a sleeve of the right main stem bronchus with the right upper lobectomy and an end-to-end anastomosis; or the removal of a sleeve of the distal trachea with the right pneumonectomy and an end-to-end anastomosis between the trachea and the left main bronchus. The bronchoscope may be used to perform bronchoalveolar lavage and brushings for cytology, as well as transbronchial biopsies under imaging guidance.

Bronchoscopy has a limited role in the assessment of mediastinal lymph nodes. Enlarged peribronchial lymph nodes may cause extrinsic airway compression and are easily biopsied transbronchially. A widened carina suggests subcarinal lymphadenopathy, which can be biopsied in a similar fashion.

The Technique—Bronchoscopy is performed with local anesthesia and intravenous sedation. A thorough examination is essential. First, the larynx and vocal cords are visualized. Immobility of a vocal cord may indicate involvement of a recurrent nerve with tumor, which is a sign of inoperability (T4).

The trachea and the carina are also assessed initially. Extrinsic compression or involvement of the trachea can be identified, and widening of the carina is highly suggestive of involved subcarinal lymph nodes. The carina is biopsied if it is thickened or there is a suggestion of submucosal extension of the tumor.

Complications—The complication rate for flexible fiberoptic bronchoscopy is 0.08%, and mortality is 0.01%.[9] Premedication and topical anesthesia are responsible for a large portion of the complications, including respiratory depression.

Massive bleeding may occur in patients with bleeding dyscrasias, which should be identified preoperatively and corrected. A biopsy should not be done unless the prothrombin time is over 40% of normal and the platelet count is greater than 50,000/mm³. All anticoagulants should be discontinued at least 7 days prior to the performance of bronchoscopy.